Framing Question: uneven ceilings
An amateur (me!) has a very basic framing question for you:
If you have a central bearing wall dividing two rooms with unequal ceiling height, it’s clear that the ceiling joists for the higher ceiling bear on the double top plate of the bearing wall. But how are the ceiling joists for the lower ceiling attached to the bearing wall? Assuming the joists are on different spacings than the studs, is it as simple as nailing a ledger board (rim joist? stringer? sorry- don’t know the correct terminology!) to the studs, and installing the joists using joist hangers- or am I missing something? Where would I find out how many nails of what size are needed to attach this ledger/rim joist to the studs? Note that in my case, the low ceiling joists are just bearing the dead load of the ceiling- there’s no storage or occupancy above. They’re not acting as collar ties for the roof framing, so there’d be no force acting to withdraw the ledger/rim joist nails from the studs- they’d be in plain shear.
Replies
That ledger board design should work.
The problem with using the hangers is that you would wind up with an awkward corner in this case, since the bottoms of the joists would not be flush with the bottom of the ledger. One way around this is to notch the ends of the joists to compensate for the drop of the hangers.
If they are not load-bearing, perhaps you could change the spacing such that the joists could be tacked onto the sides of the studs. Might be faster. Depends what is going on on the other end, I suppose.
csnow: thanks for the reply. Since both ceilings and the short piece of bearing wall above the low ceiling will be insulated, I was trying to avoid all that insulation notching at the joist/stud joints by using the ledger board. But your point about the unpleasant corner is well taken. Notching all the ceiling joists to allow for the hangers to get a nice corner would be a fair bit of work too, if a little less itchy.
Is this new construction? Are the walls open? If so, I would nail them to the studs in the bearing wall--no plate, ledger, hangers. Good enough to support a ceiling. Unless you're going to be walking up there...
Otherwise, I like the ledger/hanger plan and wouldn't worry about the funny corners. The little elevation change from the thickness of the metal hangers is well within any framing tolerance for ceilings but if you're concerned, the suggestion of notching the joists is a good one.
As far as the nailing schedule goes, you can face nail through the back of the ledger board if you want, and then just put one nail in each hole in the hangers. I use joist hanger nails for all the straight in holes that go into the side of a 2x board and 12 or 16d nails on the angled ones that go through both boards.
Thanks, Mad Dog. I'm preparing approval plans for an addition (I'll be doing the work myself), and this detail will show up in part of a structural section I'm drawing so I want to show it right.
The bearing wall is new construction, between the 2nd floor of a new addition and the existing 1.5 storey house. The addition will have a high ceiling, and the low ceiling is in some in-fill work: a pair of walk-in closets built out of what used to be knee-wall closets in the existing house. The back walls of the closets will be the old knee walls, extended to bear the closet ceiling joists. The old rafters will be trimmed, so the knee walls will now (officially) be bearing the load of the rafters (the knee walls have double top plates and proper stud spacing to act as proper bearing walls). The space above the closet ceilings, above the knee walls, and ~ 2' of the bearing wall above them, will be insulated (i.e. they'll be part of the new combined ventilated attic space). Since I'm altering the structure of the existing building, I need to show the new combined structure in my plans so the permit approvals guys can review what I'm doing.
The concern wasn't really with "what would be strong enough not to fall down", but rather with "what's normall done", or "what the building plan reviewer and the inspector will accept". Nailing through the sides of the joists into the studs will definitely work fine- I presume three common framing nails each would be more than enough. I'm just worried that the inspector guy would give me a hard time for doing it that way and make me rip it out and use hangers! They're pretty tough on DIY people up here (mostly for good reason).